Conventionally, as a technology for directly detecting property of fuel, there is proposed a detecting apparatus which detects viscosity and specific gravity of inspection object fuel from a refractive index thereof (Japanese Patent Laid-Open No. H10-19775 (1998)). However, this detecting apparatus has the structure which is complicated and expensive, and therefore, is far from being practical.
On the other hand, there are provided an apparatus which calculates a heat release quantity parameter correlating with a combustion rate based upon a pressure and a volume of a combustion chamber to measure a cetane number of fuel based upon a change of the heat release quantity parameter in a given operating condition (Japanese Patent Laid-Open No. 2005-344550), an apparatus which measures a cetane number of fuel based upon a period until the fuel is ignited (Japanese Patent Laid-Open No. 2005-344557, and an apparatus which measures a lower heating quantity of fuel to determine property of the fuel (Japanese Patent Laid-Open No. S64-88153 (1989)).
However, the measurement accuracy of each of these conventional technologies is not necessarily satisfactory. In addition, in recent years, fuel for an internal combustion engine has been diversified as, for example, bio fuel or GTL (gas liquid fuel), and therefore, it is desired to accurately determine fuel components even in such various kinds of the fuel.
Therefore, an object of the present invention is to provide means for accurately determining fuel property.